For many applications it is desirable to provide a combination clutch and brake which, although a single unit, can be electromagnetically actuated to couple a driven element with a shaft or to brake rotation of the shaft.
Such drives are particularly effective in textile machinery and must be capable of transmitting or absorbing high torques, must be operable practically free from inertia, must be rapidly switchable, must have a relatively low moment of inertia when coupling the driven element to the shaft, and must occupy a minimum of space, while being easily mounted and replaced and having long life even under low maintenance conditions.
In addition, the units must be relatively strong and capable of being switched over rapidly from drive to brake modes without the sudden changes in direction and in a manner of torque transmission detrimentally affecting the mutual positioning of the critical elements or the mechanical stability of the structure.
It has already been proposed to provide a combination clutch and brake for the purposes described in textile machine applications and in general such units are made by assembling two electromagnetic units in a mirror symmetrical relationship, i.e. back to back so that one is effective as a clutch while the other is effective as a brake. Various combinations of electromagnetic devices have been used for this purpose (see Siemens Catalogue KB Part 8, 1978, page 10). This publication describes a system in which the magnetic body is juxtaposed with a magnetic disc on the brake side which is nonrotating and with an armature disc on the clutch side which is coupled to the driven member.
The two rotors are mounted upon the shaft and clamp the bearing between them.
The assembly has relatively large axial dimensions and mounting it can bring about binding of the bearings. Maintenance and dismounting are complex.